A. Field of Invention
This invention relates to an improvement connected with the production of polyurethane foams which are obtained from reaction mixtures containing halogenated phosphate polyester additives. More particularly, the improvement pertains to the reduction or elimination of scorching in such foams.
B. Description of the Prior Art
Various phosphorus-containing, halogenated compounds have been used as additives to reduce the combustibility of polyurethane foams. For this utility, certain halogenated phosphate polyesters have been found to be particularly effective. See U.S. Pat. No. 3,817,881; No. 3,707,586; and No. 3,157,613.
However, in some commercial applications, particularly in the preparation of flexible foam from formulations containing a relatively high level of water, the inclusion of these additives may cause scorching in the cured polyurethane foam product. This is usually evidenced by noticeable foam discoloration which, if pronounced or severe, often is indicative of structural weaknesses in the foam body. Moreover, severe or pronounced discoloration, in itself, is undesirable from an appearance and product marketability standpoint. See U.S. Pat. No. 3,214,397 for a more detailed description of this scorching problem.
Further in the prior art, a number of additives have been proposed to eliminate or reduce this scorching phenomenon. Most pertinent hereto is U.S. Pat. No. 4,045,378 which teaches the use of hydroquinone as a scorch inhibitor in polyurethane foams containing halogenated phosphate polyester additives.